The tensile properties of extruded Mg-8Sn-1Zn alloys subjected to different heat treatments have been investigated. At room temperature, the alloy heat-treated at 500°C showed higher strength and ductility than the alloy heat-treated at 420°C. At 200°C, the former showed much larger tensile elongations than the latter, exhibiting 670% at a strain rate of 1.0 × 10-4 s-1. The better tensile properties in the former are attributed to grain refinement and the larger quantity of fine Mg2Sn particles.